This disclosure relates to a ram air turbine assembly that includes a lock plunger that prevents the turbine from rotating when stowed, as well as reducing the axial play of various turbine components when stowed.
A typical ram air turbine assembly includes a turbine supported by a support structure that is movable between a stowed position and a deployed position. The turbine encloses a governor assembly within a turbine hub. A rotating housing portion is connected to the turbine hub and a non-rotating housing is connected to the support structure. A lock plunger is used to prevent the turbine from rotating when in the stowed position.
The governor components are configured to have a certain amount of axial free play when in the deployed position. The governor components are preloaded in a start position by a relatively low force start spring, i.e. a 50 pound preload, for example. However, when in the stowed position, vibrations can overcome the start spring preload which can cause the components to hammer axially inside the turbine as a result of the axial free play. Engine wind milling vibrations, high level short duration (HLSD) vibrations, or random vibrations can cause this hammering effect. During an aircraft engine blade loss event, severe HLSD vibrations occur first as the engine spools down. Then, as the engine continues to turn due to air loads, a high unbalance load continues to drive longer duration wind milling vibrations. Either or both of these vibrations could significantly reduce the fatigue life of ram air turbine components.
As known, wind milling is generally unpowered aircraft engine rotation that occurs at frequencies below most ram air turbine resonant frequencies. However, HLSD vibrations are high level resonant vibrations where one or more ram air turbine modes are excited to resonance as the engine spools down resulting in high loads through the ram air turbine housings. As the aircraft engine speed decreases, the excitation frequency experienced by the ram air turbine sweeps from high to low frequencies, passing through normal ram air turbine frequencies during the decrease. Thus, these types of vibrations cause a hammering effect that can result in damaging impact loads.